This invention relates to a system for automatically determining when a person under safety surveillance has exceeded safety limits, such as, for example, where a person has fallen overboard from a boat.
There has long been a need for a system capable of monitoring the location of crew members or passengers on a boat, and for automatically emitting an alarm signal when such a person has fallen overboard. In a worst case scenario, if a person were to fall overboard at night, when the event cannot be visually observed, it is vital that an alarm be sounded or given substantially immediately, before the separation between person and boat becomes too great. Various systems have been devised to accomplish this, some of which rely upon some sort of alarm transmission device attached to the person which sends a signal to a central station, which in turn responds in any of a variety of ways.
One such device is shown in U.S. Pat. No. 3,588,858 of Demouth, in which a radio transmitter on the person is actuated by a position sensitive switch, to create an alert or alarm situation when the person is in an abnormal position.
A more sophisticated overboard detecting arrangement is shown in U.S. Pat. No. 4,305,143 of Simmons et al in which an ultrasonic transmitter attached to the person is actuated by a hydrostatic switch, i.e., a switch that actuates when in water, to send ultrasonic signals through the water to a receiver on the boat. The receiver, in turn, takes action to sound an alarm, eject life preservers, stop the boat, or some other action aimed at initiating rescue operations.
U.S. Pat. No. 4,549,169 of Moura et al shows an arrangement wherein each person carries a radio transmitter on some portion of the body that will be submerged if the person falls overboard. Each transmitter continually transmits to a monitoring station, or, in one embodiment, responds to an encoded interrogation signal from the monitoring station. When a person falls overboard, the transmitter is submerged, and thus the monitoring station receives no more signals from it, thereby indicating that the person is in the water.
In U.S. Pat. No. 4,442,426 of Heuschmann et al, a monitoring system is shown in which a plurality of remote transmitter stations send signals to a central monitor in time staggered sequence. Each signal may be coded to identify the remote transmitter. When a danger situation arises, an alarm signal is sent without delay, breaking into the sequential pattern and thus informing the central monitor of an alarm condition.
In all of the foregoing prior art patents, an alarm or danger condition is indicated when it occurs, and, in some instances, the central station is capable of taking some sort of rescue or danger alleviating action. None of the patents shows a system capable of doing more than, say, stopping the boat or ejecting life preservers. Furthermore, if a person were to fall overboard at night and perhaps be knocked unconscious, there is no way of ascertaining any of the vital information relating to his location and distance from the boat. The only indication given by any of the aforementioned devices is that the person is in the water.